feat: add server default locale setting (#1536)

* feat: add server default locale setting

* fix: do not modify defaultLocale property of IntlProvider

server/lib/settings.ts

@@ -88,6 +88,7 @@ export interface MainSettings {
   originalLanguage: string;
   trustProxy: boolean;
   partialRequestsEnabled: boolean;
+  locale: string;
 }
 
 interface PublicSettings {
@@ -106,6 +107,7 @@ interface FullPublicSettings extends PublicSettings {
   cacheImages: boolean;
   vapidPublic: string;
   enablePushRegistration: boolean;
+  locale: string;
 }
 
 export interface NotificationAgentConfig {
@@ -249,6 +251,7 @@ class Settings {
         originalLanguage: '',
         trustProxy: false,
         partialRequestsEnabled: true,
+        locale: 'en',
       },
       plex: {
         name: '',
@@ -411,6 +414,7 @@ class Settings {
       cacheImages: this.data.main.cacheImages,
       vapidPublic: this.vapidPublic,
       enablePushRegistration: this.data.notifications.agents.webpush.enabled,
+      locale: this.data.main.locale,
     };
   }